a. Scope of the invention
This invention relates to the separation and recovery of various components of the cathode effluent or "purge" from the electrolytic manufacture of a dimerized product such as adiponitrile from an olefinic compound such as acrylonitrile. More particularly, it relates to a process for the separation and recovery of the olefinic compound, the dimerized product, conductive salt and quaternary ammonium (directive) salt contained in the cathode effluent from the electrohydrodimerization of an olefinic compound, as recovery of these constituents relate to the purge rate of the cell (the speed with which the aqueous solution is evacuated from the cell and the corresponding speed with which the aqueous solution in the cell in replenished) and maintenance of process water balance as an overall electrohydrodimerization process improvement and an improved recovery process.
b. Prior art
It is well known to purge electrolytic (aqueous solutions from electrohydrodimerization reaction cells, and to recover the dimerized product, the conductive salt, and/or other recoverable reactants. The extraction of acrylonitrile and quaternary ammonium cations from electrolytic solutions is taught, for example, in Canadian Pat. No. 803,6ll, where the aqueous solution, described as an aqueous mixture, was decanted into an organic phase and a water phase, the former comprising adiponitrile and acrylonitrile, the latter comprising quaternary ammonium salt.
It is also well known to extract acrylonitrile from cathode effluent with adiponitrile, and to use water for the extraction of quaternary ammonium salt from the organic (oil) phase of a two-phase electrolyte system or a quasi biphase elctrolyte system, such as that described in Canadian Pat. No. 803,611 (in which decantation is necessary to separate phases), or from a substantially unphased aqueous solution.
It is also known to crystallize the cathode effluent in order to recover the conductive salt (see U.S. Pat. No. 3,267,131).
The speed at which a commercial dimerization process can be efficiently and economically operated depends in large part upon the efficiency and speed of the recovery subsystem with respect to which prior art procedures, collectively employed, have failed to keep pace with developments related directly to operation of the electrolytic cell.
An efficient coordinated recovery system in which a rate of purge, and replenishment of the electrolyte which permits of substantial reconstitution of the electrolyte with recoverable components at the required rate and with minimum losses of recoverable components, would permit maximum productivity of the electrolytic cell, would constitute a significant advance in the art and is an object of this invention.